Alpha-methylstyrene (AMS) is mainly used as a comonomer for high heat resistance and for improving impact physical properties of acrylonitrile butadiene styrene (ABS), polystyrene (PS) and acrylic resins, and in addition, is used as a coating agent, adhesives, cumylphenol, wax, or the like. Such alpha-methylstyrene (AMS) is mostly produced commercially as the by-products of a cumene (CM) oxidation reaction in a bisphenol-A (BPA) process, and also, as shown in Reaction 1 below, may be obtained by the dehydrogenation reaction of cumene, which is not used commercially.

However, the method is very similar to the production technique of styrene (SM; styrene monomer) in which ethylbenzene (EB) is dehydrogenated in view of technical aspect, as shown in Reaction 2 below, and by-products mainly include materials produced during preparing styrene (SM), such as toluene, ethylbenzene and styrene. Thus, alpha-methylstyrene may be obtained with low investment costs by modifying the conventional preparation process of styrene and feeding ethylbenzene and cumene concurrently to produce styrene and alpha-methylstyrene (AMS) concurrently when compared to a case of producing solely.

Meanwhile, FIG. 1 is a diagram partially showing a common styrene preparation process. Styrene (SM) is prepared by reacting ethylbenzene (EB) and undergoing processes such as condensation and fractional distillation. Since the difference of boiling points between ethylbenzene and styrene is small, a lot of energy is required for the separation of EB/SM. In order to solve this, as shown in FIG. 1, instead of using a utility such as steam in a reboiler of EB/SM separation column, waste heat in a process is utilized, or heat of a condenser is recovered and utilized instead of steam. Generally, recovered heat from the condenser of EB/SM separation column is used for the vaporization of ethylbenzene which is injected to a reactor, and in this case, an azeotropic mixture of ethylbenzene/water is vaporized to decrease a vaporization temperature and increase heat recovery. Accordingly, a highly economic method for producing styrene and alpha-methylstyrene concurrently and for decreasing the amount of energy consumed for the production is required by modifying the conventional styrene process.